Nanobubble ozone treatment effects on cyanobacterial biomass and cyanotoxins in a small eutrophic lake

Cyanobacterial harmful algal blooms (CHABs) fueled by excessive nutrient runoff are becoming an increasing problem worldwide. Nanobubble ozone technology (NBOT) is an emerging treatment to remediate lakes from CHABs. NBOT was tested in Lake Sylvan, a 42-acre manmade eutrophic lake that experiences annual CHABs. NBOTs were deployed from 7 July to 17 September 2021, and dosage was tripled on 9 August. CHAB chlorophyll, microcystins, and saxitoxins (among other parameters) were measured June to October 2021, spanning pre-NBOT, NBOT deployment, and post NBOT treatment. CHAB chlorophyll increased throughout July (peaking at 100 μg/L) then sharply declined following the increased dose (25-35 μg/L) but increased again 3 weeks (51-78 μg/L) after increased dose. CHAB chlorophyll spiked (80-95 μg/L) in early October after NBOT treatment. Microcystins steadily increased from <0.15 to 2.5 μg/L throughout June and July and remained between 0.4 to 1.0 μg/L August – October. No contact advisories were posted during 2021 unlike previous years. Total saxitoxins rapidly increased in mid-July peaking at 4 μg/L, and then declined. Several large rainstorms (10 cm/d) occurred during NBOT treatment which may contributed nutrients. These storms complicated the evaluation of NBOT efficacy. Lake Sylvan will be monitored in 2022 without NBOT treatment for baseline conditions.